while loop will not execute

Question

I need a while loop to only take in positive number. I wrote a while loop but it won't execute and Im not sure what's wrong. My code works fine with a for while loop but when I enter a negative number and run the code it prints out the input, then reprompts the user. I just want it to re-prompt, not print the input too.

Thank you if anyone can help.

This will print the input, then reprompt the user

#include <cs50.h>
#include <stdio.h>

int main(void)

{
    float change;

    do
    {
        change = get_float("Change: ");
        printf("%f\n", change);
    }
    while (change < 1);

}

This will not execute at all

#include <cs50.h>
#include <stdio.h>

int main(void)

{
    float change;

    while (change < 1)
    {
        change = get_float("Change: ");
        printf("%f\n", change);
    }


}

@ChetanRanpariya: Objects with automatic storage duration are not initialized by default. — Eric Postpischil, Aug 25 '19 at 00:35
I am not a C expert... But in C# it works like that. That's why I explained why while loop is not executing. — Chetan, Aug 25 '19 at 00:39

score 0 · Answer 1 · answered Aug 25 '19 at 00:28

0

In the first one, just stop doing the printf inside the loop.

In the second one, you're testing the value of change before you store a value in it, which is Undefined Behavior.

answered Aug 25 '19 at 00:28

Joseph Sible-Reinstate Monica

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where should float change be moved to? – Dkirch Aug 25 '19 at 00:31
Ok ill give it go. Thanks for helping. – Dkirch Aug 25 '19 at 00:38

Mudassir Hasan · Accepted Answer · 2019-08-25T00:41:58.807

Try below. check the comments for explanation

Using do..while loop

#include <cs50.h>
#include <stdio.h>

int main(void)

{
    float change;

    do
    {
        change = get_float("Change: ");

    }
    while (change < 1);
    printf("%f\n", change);

}

Using while loop

#include <cs50.h>
#include <stdio.h>

int main(void)

{
    float change;
    change = get_float("Change: "); //Capture value for first time
    while (change < 1) //Check if input value is negative
    {
        change = get_float("Change: "); //If negative ask for input again

    }

    printf("%f\n", change); // If value is positive, while loop passed over and value printed


}

while loop will not execute

2 Answers2